This invention relates to the field of display systems, more particularly to color correction of display systems, particularly display systems using primary color sources to generate full color images.
Image display systems create images for a human viewer to experience. The goal of the display systems is to simulate the experience of being at the location being displayed. These locations may be real, for example when a scene is recorded using a camera, imaginary, for example when a computer generates a scene using a database of shape and texture information, or a combination of real images and superimposed computer generated images.
Regardless of the source of a particular image, the display system must be able to recreate the complex color tones and intensities in order to make the recorded image appear life-like. To do this, the color spectrum of the display system must be correlated to the color spectrum of the device used to capture the image. This can be a particular challenge when displaying an image initially recorded on a subtractive color media such as cinemagraphic film on an additive color-based system such as a CRT, LCD, or DMD display.
Color is a perceptual characteristic, requiring a human viewer. The perceived color of an object is determined by the spectral power distribution of the light emitted by or reflected by the object and the response of the human visual system. The human eye contains sensors, called rods and cones, that detect the light from the object focused on the retina. Rods are responsible for low light vision. Cones are responsible for color vision. There are three types of cones in the human eye, each with a distinct pass band. Using the output from the three types of cones, the human brain creates the perception of color and intensity for each portion of an image.
Subtractive color systems and additive color systems create the sensation of color for each portion of an image in opposite manners. Subtractive color media, such as photographic film, use dyes to absorb the unwanted portions of the spectrum of light from a source while reflecting or transmitting the portions needed to create an image. Additive color systems, such as CRT and micromirror displays, source primary colored light to an image. Neither color system recreates the entire spectrum of the original image, but instead creates the perception of the original image by stimulating the three types of cones to produce a perceptual response that is the same as provided by the original spectrum. Thus, three or more carefully chosen light sources (e.g. red, green, and blue) can be used to provide the perception of a continuous color spectrum.
The three colors chosen to be the primary colors of an additive color display system determine the available color space of the display system. While a given set of primary colors may provide a very broad color space, the use of filters to select the given set of primary colors from a white light beam often limits the maximum intensity the display system is capable of producing to less than a minimum acceptable amount. Likewise, a given selection of color filters may result in a white level, formed by combining the primary colors, that has an undesirable color tint.
While an ideal display can create a high intensity display of very pure colors including white, real world display systems must make tradeoffs between the white level, purity of the primary colors, and the maximum available brightness. These tradeoffs affect the secondary colors since the secondary colors are formed by combining two or more primary colors. Thus, once the primary color filters are selected, the white point and the purity of the secondary colors is also determined.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for the enhanced color correction of image data. One embodiment of the claimed invention provides a method of correcting color image data for a pixel. The method comprising the steps of: providing intensity data for three primary colors, three secondary colors, and a neutral color for the pixel; providing a set of matrix coefficients for each output primary color, one said coefficient for describing the contribution said output primary color makes to each of the primary, secondary, and neutral colors; and summing the products of the matrix coefficients and corresponding intensity data to provide a corrected intensity data value for each output primary.
According to a second embodiment of the disclosed invention, a method of correcting color image data for a pixel is disclosed. The method comprising the steps of: providing image data for the pixel, converting the image data to a color space having a primary, secondary, and neutral color component; providing coefficients describing the contribution made each of three output primary colors to the formation of said primary, secondary, and neutral color components; and summing the products of said coefficients and said primary, secondary, and neutral color components to provide a corrected intensity data value for each output primary.
According to yet another embodiment of the disclosed invention, a method of correcting color image data for a pixel is disclosed. The method comprising the steps of: providing image data for said pixel; converting said image data to a color space having a primary (P), secondary (S), and neutral (N) color component; selecting a set of coefficients describing the contribution of the primary, secondary, and neutral components to the output primaries, and calculating a corrected output value for each said output primary according to the following equation:       [          xe2x80x83        ⁢                                        R            xe2x80x2                                                            G            xe2x80x2                                                            B            xe2x80x2                                ⁢          xe2x80x83        ]    =            [              xe2x80x83            ⁢                                                  X              RP                                                          X              RS                                                          X              RN                                                                          Y              GP                                                          Y              GS                                                          Y              GN                                                                          Z              BP                                                          Z              BS                                                          Z              BN                                          ⁢              xe2x80x83            ]        ⁢          xe2x80x83        [          xe2x80x83        ⁢                            P                                      S                                      N                      ⁢          xe2x80x83        ]  
where:
XRP is the contribution of the primary color component to a first output primary (Rxe2x80x2)
XRS is the contribution of the secondary color component to the first output primary (Rxe2x80x2)
XRN is the contribution of the neutral color component to the first output primary (Rxe2x80x2)
YGP is the contribution of the primary color component to a second output primary (Gxe2x80x2)
YGS is the contribution of the secondary color component to the second output primary (Gxe2x80x2)
YGN is the contribution of the neutral color component to the second output primary (Gxe2x80x2)
ZBP is the contribution of the primary color component to a third output primary (Bxe2x80x2)
ZBS is the contribution of the secondary color component to the third output primary (Bxe2x80x2)
ZBN is the contribution of the neutral color component to the third output primary (Bxe2x80x2)
The disclosed methods and systems provide independent control over the primary and secondary image colors, as well as over the neutral color componentxe2x80x94typically the white level. As implemented, the described methods and systems require very little additional processing power compared to traditional color correction matrixing approaches, and therefore can be implemented in real time without excessive cost.